Gallium nitride (GaN), a wide bandgap semiconductor, has received significant interest and investment from educational, governmental, and industrial entities due to the potential for fabricating advanced optical and electrical GaN-based semiconductor devices. Beginning in the early 1990's, researchers have made continuous progress in researching developing, improving, and ultimately commercializing GaN-based semiconductor devices, including green and blue wavelength light emitting diodes (LEDs), blue wavelength laser diodes (LDs), and high-speed and high-power metal-semiconductor field effect transistors (MESFETs), high-electron mobility transistors (HEMTs), and power transistors.
While significant progress has been made in the development of Group-III nitride (hereafter, “III-nitride”)-based semiconductor devices, further improvements in device materials, structures, and methods of fabrication are needed to realize the full potential, in terms of device performance, efficiency, and cost metrics, of III-nitride-based devices. Therefore, there is an unmet need in the industry for materials, structures, and methods for improving the performance, efficiency, and cost of III-nitride-based semiconductor devices. In addition, there is a further unmet need in the industry for a so-called metal-base transistor, which has been commercially unavailable do to the difficulty in forming high-quality semiconductor/metal/semiconductor epitaxial structures.